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Table 2 Methodological information for dealing with zero-events studies

From: Utilization of the evidence from studies with no events in meta-analyses of adverse events: an empirical investigation

Methodological information for dealing with zero-events studies Yes (%, exact CI) No (%, exact CI) NC or NA (%, exact CI) Total
1) In the systematic review, did any meta-analysis contain zero-events studies? 406 (63.44, 59.57 to 67.18) 88 (13.75, 11.18 to 16.66) 146 (22.81, 19.62 to 26.26) 640
2) If zero-events studies were involved, what were the types of zero-events studies?     406
• Single-arm-zero-events only 174 (42.86, 37.99 to 47.83)  
• Double-arm-zero-events only 7 (1.72, 0.70 to 3.52)  
• Both single and double 208 (51.23, 46.25 to 56.19)  
• At least containing single-arm-zero-events study 7 (1.72, 0.70 to 3.52)  
• At least containing double-arm-zero-events study 8 (1.97, 0.85 to 3.85)  
• Cannot be judged 2 (0.49, 0.06 to 1.77)  
3) If zero-events studies were involved, whether the authors specified methods to deal with zero-events studies? 131 (32.27, 27.74 to 37.05) 275 (67.73, 62.95 to 72.26) 0 (0.00, 0.00 to 0.90) 406
4) If the authors specified methods, whether they clarified reasons for selecting the method for zero-events studies? 44 (33.59, 25.58 to 42.36) 87 (66.41, 57.64 to 74.42) 0 (0.00, 0.00 to 2.78) 131
5) If zero-events studies were involved, how zero-events studies were dealt with by the authors? See detailed methods in Fig. 2
• Discarding single-arm-zero-events studies (174 + 208 + 7 = 389) 3 (0.77, 0.16 to 2.24) 384 (98.71, 97.03 to 99.58) 2 (0.51, 0.06 to 1.85) 389
• Discarding double-arm-zero-events studies (7 + 208 + 8 = 223) 170 (76.23, 70.09 to 81.66) 50 (22.42, 17.12 to 28.47) 3 (1.35, 0.28 to 3.85) 223
6) Whether a sensitivity analysis was employed through at least one different synthesis method for dealing with zero-events studies? 53 (13.05, 9.93 to 16.73) 353 (86.95, 83.27 to 90.07) 0 (0.00, 0.00 to 0.90) 406
7) For those failed to synthesize studies with zero-events, did the authors discuss about the potential impact of such studies (e.g., discarding them) on the results? 22 (12.94, 8.29 to 18.94) 148 (87.06, 81.06 to 91.71) 0 (0.00, 0.00 to 2.15) 170
  1. NC not clear; NA not applicable